Laboratory Services
Custom Peptide Synthesis, Built to Your Sequence
When a study needs a sequence that no catalogue carries — a point mutant, a labelled probe, a cyclised analogue, a stable-isotope internal standard — the peptide has to be made to order. This page covers how custom synthesis works end to end: the chemistry, the purity grades and what each one is actually good for, the modifications available, realistic lead times, and the documentation that ships with every lot. All peptides are supplied for in-vitro laboratory research use only.
In short: PeptidesDirect synthesises custom peptides from 2 to 50 residues by Fmoc solid-phase peptide synthesis, at scales from 1 mg to multi-gram, in purity grades from crude through >98% RP-HPLC. Modifications include acetylation, amidation, biotin, PEG, lipidation, phosphorylation, fluorescent labels and FRET pairs, D- and unnatural amino acids, disulfide bridges, and cyclisation. Standard linear sequences at >95% purity deliver in 2–3 weeks; every lot ships with an HPLC chromatogram, mass confirmation, and a Certificate of Analysis. Quotes are returned within one business day and are firm. Research Use Only.
Service Specifications
| Parameter | Specification |
|---|---|
| Chemistry | Fmoc solid-phase peptide synthesis (SPPS) |
| Length range | 2–50 residues standard; longer by consultation |
| Scale | 1 mg to multi-gram, single homogeneous lot |
| Purity grades | Crude, >75%, >85%, >95%, >98% |
| Analytics | RP-HPLC chromatogram + LC-MS / MALDI-TOF |
| Standard lead time | 2–3 weeks (linear, unmodified, >95%) |
| Documentation | Certificate of Analysis per lot |
| Use classification | Research Use Only — in-vitro laboratory use |
How the Synthesis Works
- Sequence review. Before any resin is loaded, the sequence is screened for aggregation-prone stretches, difficult couplings, oxidation-sensitive residues (Met, Cys, Trp), and Asp-Gly or Asn-Gly motifs prone to side reactions. Where a substitution or protecting-group strategy will materially improve yield, it is proposed at the quote stage.
- Solid-phase assembly. Chain elongation proceeds C-terminus to N-terminus on a resin support using Fmoc-protected amino acids, with coupling and deprotection cycles monitored for completion. Difficult sequences use pseudoproline dipeptides, double couplings, or microwave-assisted protocols.
- Cleavage and deprotection. A TFA cocktail with appropriate scavengers releases the peptide from the resin and removes side-chain protecting groups; the crude peptide is precipitated in cold ether and dried.
- Purification. Reverse-phase HPLC on C18 resolves the target from deletion and truncation products. Fractions are pooled to hit the ordered purity grade, then lyophilised.
- Verification. Identity is confirmed by LC-MS or MALDI-TOF against the calculated monoisotopic mass, and final purity is measured on an analytical HPLC gradient. Both traces are attached to the Certificate of Analysis.
- Release. The peptide ships as a lyophilised powder under desiccation with lot number, storage guidance, and reconstitution notes — see the reconstitution guide and storage guide for handling on arrival.
Choosing a Purity Grade
| Grade | Typical application |
|---|---|
| Crude | Epitope mapping, large screening libraries, ELISA blocking |
| >75% | Antibody production, immunisation antigens |
| >85% | Preliminary binding and enzyme assays |
| >95% | Standard in-vitro assays, cell-based work, SAR studies |
| >98% | Quantitative assays, NMR/crystallography, mass-spec standards |
Purity is an HPLC area-percent figure, not a mass figure. Lyophilised peptide also contains counter-ions (typically TFA or acetate) and residual water, so a >95% peptide can be 70–85% net peptide by weight. For quantitative work, order a peptide-content assay alongside the purity grade — the same principle covered in the peptide purity testing guide.
Available Modifications
Terminal
N-acetylation, C-amidation, free acid, pyroglutamate
Labels
FITC, TAMRA, FAM, Cy3/Cy5, biotin, FRET pairs with Dabcyl/QXL
Conjugation
PEG2–PEG24, C16/C18 fatty-acid lipidation, KLH/BSA carriers
Post-translational
Phospho-Ser/Thr/Tyr, methylation, acetyl-Lys, glycosylation
Architecture
Intramolecular and intermolecular disulfides, head-to-tail and side-chain cyclisation, stapled helices
Residues
D-amino acids, Aib, Nle, ornithine, citrulline, stable-isotope 13C/15N labels
Custom Synthesis vs Catalogue Peptides
If the sequence you need is already characterised and in routine use, a catalogue lot is faster and cheaper: it is in stock, third-party tested, and shipped same day. Custom synthesis makes sense when the sequence is novel, mutated, labelled, or needed at a scale or purity the catalogue does not carry. Many programs use both — catalogue material for controls and reference curves, custom material for the variable under study.
Frequently Asked Questions
What is custom peptide synthesis?
Custom peptide synthesis is the made-to-order chemical assembly of a peptide from a sequence supplied by the researcher. The sequence is built residue-by-residue on a solid support (Fmoc solid-phase peptide synthesis), cleaved, purified by reverse-phase HPLC, confirmed by LC-MS, and delivered lyophilised with a Certificate of Analysis. It differs from catalogue peptides in that nothing is held in stock — the peptide is made specifically for that order.
How long does custom peptide synthesis take?
A standard linear peptide of 5–25 residues at >95% purity is typically delivered in 2–3 weeks. Sequences of 26–50 residues, or peptides requiring disulfide bridges, cyclisation, or multiple modifications, generally run 3–6 weeks. Difficult sequences (long hydrophobic stretches, multiple beta-branched residues, aggregation-prone motifs) can extend the timeline; we flag those at the quoting stage rather than after the order is placed.
What purity levels are available?
Crude (no HPLC purification) for screening libraries, >75% and >85% for antibody production or preliminary assays, >95% for most in-vitro work, and >98% for quantitative or structural studies. Every purified lot ships with an HPLC chromatogram, an LC-MS or MALDI-TOF mass confirmation, and the net peptide content where a peptide-content assay is requested.
What modifications can be included?
N-terminal acetylation, C-terminal amidation, biotinylation, PEGylation, fatty-acid conjugation (C16/C18 lipidation), phosphorylation (Ser/Thr/Tyr), fluorescent labels (FITC, TAMRA, FAM, Cy3/Cy5), FRET pairs with quenchers, D-amino acids, unnatural and Aib residues, intramolecular and intermolecular disulfide bridges, head-to-tail cyclisation, and stable-isotope labelling for mass-spec quantitation.
What scales can be ordered?
From 1 mg for assay-scale screening up to multi-gram lots for pre-clinical programs. Milligram-scale orders ship as a single lyophilised vial; gram-scale orders are produced as a single homogeneous batch with lot-level documentation so downstream results stay comparable.
How much does custom peptide synthesis cost?
Price is driven by sequence length, scale, purity grade, and modifications rather than by a flat per-milligram rate. A short unmodified 10-mer at 5 mg and >95% purity sits at the low end; long, cyclised, or multiply-labelled sequences at gram scale sit at the high end. Quotes are returned within one business day and are firm — the price does not move if the synthesis proves difficult.
What documentation ships with a custom peptide?
Every lot ships with a Certificate of Analysis containing the sequence, molecular formula, calculated and observed mass, HPLC purity with the chromatogram, counter-ion and net peptide content where assayed, appearance, solubility guidance, and storage conditions. Analytical raw data is available on request for regulated or publication-bound work.
Is my sequence kept confidential?
Yes. Submitted sequences are treated as confidential research information, are not added to any catalogue, and are not shared with third parties. A mutual NDA can be executed before sequence submission on request.
Are custom peptides supplied for human use?
No. All peptides produced by PeptidesDirect — catalogue and custom — are supplied strictly as research chemicals for in-vitro laboratory use. They are not drugs, foods, cosmetics, or medical devices, and are not intended for human or veterinary administration.
Related Reading
Research Use Only. All custom and catalogue peptides supplied by PeptidesDirect (P Direct LLC) are chemicals intended for in-vitro laboratory research by qualified professionals. They are not drugs, foods, or cosmetics and are not for human or veterinary use.
